Tortuosity of Battery Electrodes: Validation of Impedance-Derived Values and Critical Comparison with 3D Tomography

Landesfeind, Johannes; Ebner, Martin; Eldiven, Askin; Wood, Vanessa; Gasteiger, Hubert A.

doi:10.1149/2.0231803jes

Cited by 128 publications

(156 citation statements)

References 19 publications

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“…The gray rectangle in Figure 2 depicts the tortuosity range for platelet graphite obtained using X-ray tomography for the range of porosities used in this work (51 ± 5%), which may be considered to be the theoretical lower tortuosity limit for the graphite active material if unaffected by the binder, as X-ray tomography cannot resolve the binder/conductive carbon phase and thus commonly ignores its effect on tortuosity. 5,14 By an approximate extrapolation of the tortuosities from the presented EIS measurements in Figure 2 to 0 wt% binder, limiting tortuosity values for conceptually binder-free anodes between 2.4 and 4 can be projected, which is reasonably close to the tortuosity range for electrodes estimated from X-ray tomography (1.6 to 2.0), where the binder contribution is not considered. The remaining difference might be due to different aspect ratios of the graphite particles or to the inability to sufficiently extrapolate from 1.5-3 wt% binder to 0 wt% binder.…”

Section: Resultssupporting

confidence: 52%

“…3,14 In the first part of our analysis we will demonstrate the effect of binder and conductive carbon additives on electrode tortuosity and thereafter give an overview of the range of experimentally obtained tortuosities for two water and three NMP (n-methyl-2-pyrrolidone) based binder systems. Subsequently, charging rate performance tests in three-electrode cells for electrodes with largely different tortuosities are presented, illustrating the clear correlation between the tortuosity of the anode electrode and its rate capability.…”

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confidence: 99%

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Influence of the Binder on Lithium Ion Battery Electrode Tortuosity and Performance

Landesfeind

Eldiven

Gasteiger

2018

J. Electrochem. Soc.

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114

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The electrochemical performance of porous graphite anodes in lithium ion battery applications is limited by the lithium ion concentration gradients in the liquid electrolyte, especially at high current densities and for thick coatings during battery charging. Beside the electrolyte transport parameters, the porosity and the tortuosity of the coating are key parameters that determine the electrode's suitability for high power applications. Here, we investigate the tortuosity of graphite anodes using two water as well as three n-methyl-2-pyrrolidone based binder systems by analysis of symmetric cell impedance measurements, demonstrating that tortuosities ranging from ∼3-10 are obtained for graphite anodes of similar thickness (∼100 μm), porosities (∼50%) and areal capacity (∼3.4 mAh/cm 2 ). Furthermore, selected electrodes with tortuosities of 3.1, 4.3, and 10.2 were cycled in cells with reference electrode at charging C-rates from 0. Understanding and predicting rate limitations in lithium ion batteries with porous electrodes requires profound knowledge of not only the electrolyte transport parameters (i.e., transference number, diffusion coefficient, conductivity) and the thermodynamic factor, but also the porosity and the tortuosity of the electrodes. The tortuosity of the electrode is particularly critical because the effective electrolyte conductivity and the effective diffusion coefficient in the electrolyte directly scale with the inverse of the tortuosity, so that care has to be taken to develop electrodes with minimized tortuosity. Using experimental approaches 1-4 or 3D tomography, 5,6 it was shown that the shape of active material particles distinctly influences the electrode tortuosity. For a given active material, however, electrode tortuosity and rate capability can also be improved by the design of the electrode layer such that short diffusion distances can be obtained across the electrode. For example, improved performance was demonstrated for graphite anodes when the platelet graphite particles were aligned normal to the current collector surface by means of a magnetic field 7 or when silicon/graphite anode electrodes were laser structured. 8 In this study we focus on the role of the electrode composition, specifically the role of the binder, on its tortuosity as well as on its implication for battery performance. While in the literature the link between binder and electrochemistry is frequently studied empirically using rate capability tests 9 and long-term cycling experiments, 10-13 we focus on the correlation of electrode tortuosity with binder content/type and its effect on rate capability.In the following, the tortuosity of graphite anodes with different binders, different binder contents, and different amounts of conductive carbon additive will be determined by electrochemical impedance spectroscopy (EIS) of symmetric cells using the transmission line model approach. 3,14 In the first part of our analysis we will demonstrate the effect of binder and conductive carbon additives on electrode t...

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Section: Resultssupporting

confidence: 52%

mentioning

confidence: 99%

Influence of the Binder on Lithium Ion Battery Electrode Tortuosity and Performance

Landesfeind

Eldiven

Gasteiger

2018

J. Electrochem. Soc.

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114

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“…The first high frequency semicircle is due to formation of SEI film and the middle frequency semicircle is due to charge transfer resistance at the interface of electrode and electrolyte and double layer capacitance. [36,37] However, in the current scenario, the presence of amorphous carbon network around Si-NPs prevents them from delaminating. For better understanding about the composite system, EIS was performed on the fully delithiated cell.…”

Section: Electrochemical Performance Of the Tailored Composite Gcsi Amentioning

confidence: 90%

“…[34] The straight line indicates the diffusion of lithium ions. [37] As shown in Figure 5E, the first-cycle gravimetric discharge capacity of GCSi composite was 1126 mAh g −1 with a Adv. As shown in Figure 5D, the series resistance (R s ) for the freshly constructed cell was 2.5 Ω, which remained consistent even after the 1st cycle.…”

Section: Electrochemical Performance Of the Tailored Composite Gcsi Amentioning

confidence: 92%

In Situ Mechanistic Elucidation of Superior Si‐C‐Graphite Li‐Ion Battery Anode Formation with Thermal Safety Aspects

Parekh

Sediako

Naseri

et al. 2019

Advanced Energy Materials

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understanding of the material synthesis/ fabrication, interfacial behavior, and thermal-chemical stabilities are vital. [3] With electronic appliances requiring stable voltage delivery, the current LIBs employ graphite or mixtures with soft carbons (carbon black) to achieve stable performance at discharge curves. [4] Since 1991, various forms of ordered and disordered (i.e., soft and hard) carbon have been primarily used as anode materials. [5] With graphitic carbon, a compromise was identified, which delivered a theoretical maximum capacity of 372 mAh g −1 , while maintaining stability and cycling characteristics. This stability comes at a cost of battery capacity, as it takes six carbon atoms to bind a single lithium ion (LiC 6 ) during charging process. [6] By contrast, alternative anode materials such as silicon, can bind about four lithium atoms (SiLi 4.4 ), improving energy densities by an order of magnitude. [7] Silicon anodes have garnered huge attention as they provide over ten times more theoretical capacity (3579 mAh g −1 ) than graphite anode. Problematically, the intercalated Si, Li 3.75 Si, swells in volume by about 320% during charging. Such huge volumetric expansion causes large material stresses, resulting in anode cracking, fracturing, loss of electrical contact (delamination), unstable solid electrolyte interface (SEI) and even catastrophic cell failure. [8][9][10][11] Naturally, this is unacceptable for practical and industrial applications. To overcome the capacity limitations of carbon, and the mechanical limitations of silicon, manufacturers have moved into composite materials-with the primary structure consisting of graphitic carbon, with silicon nanoparticles implanted within. First reported by Yoshio and co-workers in 2002, the C/Si composites did improve capacity, but the silicon nanoparticles were difficult to merge with the carbon bulk. [12,13] After repeated cycling, it was found that the particles separate and capacity drops. [14] Li et al. reported fabrication of graphite-Si composite using polymer blends of poly(diallyl dimethyl-ammonium chloride) and poly(sodium 4-styrenesulfonate) to obtain capacity of 450 mAh g −1 with 95% capacity retention after 200 cycles. [15] Zhang et al. prepared core-shell structure (Si@C) using silicon nanoparticles (Si-NPs) and emulsion polymerization of acrylonitrile, followed by pyrolysis. [16] The composite [15] retained A composite anode material synthesized using silicon nanoparticles, micrometer sized graphite particles, and starch-derived amorphous carbon (GCSi) offers scalability and enhanced electrochemical performance when compared to existing graphite anodes. Mechanistic elucidation of the formation steps of tailored GCSi composite are achieved with environmental transmission electron microscopy (ETEM) and thermal safety aspects of the composite anode are studied for the first time using specially designed multimode calorimetry for coin cell studies. Electrochemical analysis of the composite anode demonstrates a high initial discharge capaci...

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“…[58] Only the 3 %wt catalyst layer deviates from this pattern preserving in-plane conductivities of ≈1 S cm −1 under liquid water conditions. The conductivity dropped by up to two orders of magnitude, indicating structural changes in the electrical percolation network.…”

Section: Elucidating the Mechanistic Of The Mpl Effectmentioning

confidence: 94%

Hierarchically Structured Porous Transport Layers for Polymer Electrolyte Water Electrolysis

Schuler

Ciccone

Krentscher³

et al. 2019

Advanced Energy Materials

132

162

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renewable power, from wind or solar by medium-to-long-term storage using hydrogen as the energy vector, [1,2] enabling effective decarbonisation of the energy sector. [3] PEWE converts electric power by electrochemical water splitting into storable chemical energy. [4][5][6][7] Hydrogen can be reconverted to power or used in other sectors, [8,9] such as fuel cell based mobility [10] and chemical industries. [11] To make hydrogen production with polymer electrolyte water electrolysis a technoeconomically relevant contender, capital and operational cost need to be reduced substantially. [12][13][14][15] Operational cost, which becomes the main cost driver for operation schemes with high duty ratio (≥6000 h p.a.), is governed by power prices and the hydrogen production efficiency of the PEWE plant, which in turn strongly depends on the electrochemical performance and efficiency of the PEWE cell technology employed. [16] The electrochemical efficiency is governed by the underlying electrochemical loss mechanisms of kinetic, ohmic, and mass transport losses, whereas capital cost is driven by limited power density and high noble metal catalyst loadings.Recent studies revealed that the structure of the interface between the anodic porous transport layer (PTL) and the catalyst layer (CL) is a crucial factor limiting cell efficiency. [17][18][19][20][21] Today's PEWE technology relies on porous, Ti based, transport layer materials in the form of sintered materials [17,18,[22][23][24][25] with original applications in filtration [26] or medical tissue growing. [27][28][29] The lack of PTL materials with suitable surface characteristics tailored for this application inhibits the further improvement of cell efficiency and development of PEWE technology.Kinetic losses are governed by the sluggish kinetics of the oxygen evolution reaction (OER). The related overpotential depends on intrinsic catalyst parameters, such as specific exchange current density, activation energy, and number of active catalyst sites. [30] It has been established with model experiments such as optical imaging of the PTL/CL interface [19,20,31] and correlation of in-depth electrochemical analysis with PTL surface structure [17,18] that the catalyst is only partially utilized and CL domains not directly contacted by the porous Timaterials showed no gas evolution hence no electrochemical activity. Schuler et al. [17,18] have quantified the effect, showing

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Tortuosity of Battery Electrodes: Validation of Impedance-Derived Values and Critical Comparison with 3D Tomography

Cited by 128 publications

References 19 publications

Influence of the Binder on Lithium Ion Battery Electrode Tortuosity and Performance

Influence of the Binder on Lithium Ion Battery Electrode Tortuosity and Performance

In Situ Mechanistic Elucidation of Superior Si‐C‐Graphite Li‐Ion Battery Anode Formation with Thermal Safety Aspects

Hierarchically Structured Porous Transport Layers for Polymer Electrolyte Water Electrolysis

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